The National Weather Service posted excessive heat warnings for much of the nation's midsection, including Illinois, Wisconsin, Minnesota, Iowa, Missouri, Kansas, Nebraska, Oklahoma, as well as South and North Dakota, where forecasters predicted heat indexes could hit 115 degrees Fahrenheit.

"This will likely be the most significant heat wave the region has experienced in at least the last five years," the weather service said.

But be warned, east coasters will not be spared.

By mid week many locations on the East Coast will have heat index values approaching or exceeding 100 degrees, including Washington, D.C., the weather service said.